Permanent magnet and method of manufacturing same



April 9, 1935. Y. KATO EIAL 1,997,193

PERMANENT MAGNET AND METHOD OF MANUFACTURING SAME Filed June 16, 1932Fig.4

N .S N S iii-iiiii" if}; g/v 5 N 7 gmeniozs YOSOFO iatented Apr. 9, 1935UNITED STATES PATENT OFFICE PERMANENT MAGNET AND METHOD OF MANUFACTURINGSAM'E Application June 16, 1932, Serial No. 617,520

In J

8 Claims.

Our invention relates to improvements in permanent magnets and moreparticularly to those consisting of a coherent body of metal oxides.

Permanent magnets have heretofore been made of solid blocks of metallicalloys, such as carbonsteels. Carbon-steel containing about 1.2% ofcarbon by weight, has relatively high retentivity, and cobalt-steelalloy is also well-known as having good properties as a permanentmagnet. However, it is very diificult to form these metallic alloys,especially cobalt-steel alloy, into desired shapes and dimensions,particularly for strong permanent magnets.

In order to facilitate the formation of permanent magnets, it has beenproposed to utilize granular metals or metal powders in an agglomeratedform, but no satisfactory result has been obtained, mainly due to oxidefilm covering the metal particles, which film obstructs the magneticproperty. We have found that, if certain kinds of metal oxides, forexample, iron oxide and cobalt oxide, are combined or united together inpowdered form and made into a compact or coherent body through suitabletreatment as described hereinafter, a very good material for permanentmagnets is obtained, with an extremely high coercive force, as high asfive times that of the above-mentioned carbon-steel alloy. We have alsofound that if iron oxide and cobalt oxide in powdered form are mixedintimately and made into a compact body andtreated as hereinafterdescribed, a similar superior magnet is obtained.

Our improved magnet has many other advantages. Since the materials areoxides of metals, there will be practically no further oxidation of themagnet body at ordinary temperatures resulting in the formation of rust.Our improved magnets are made in coherent agglomerated form, and may beformed into any desired shapes and dimensions in a relatively simple andeconomical way. Our improved magnets are also economical to manufacturebecause practically all waste is eliminated.

It is, therefore, an object of our invention to provide permanentmagnets with high coercive force.

Another object of our invention is to provide permanent magnets whichare not oxidized materially to rust.

A further object of our invention is to provide a method ofmanufacturing permanent magnets in a simple and economical manner.

A still further object of our invention is to obtain a permanent magnetwith its poles at any desired spots or area of the body, such selectiveapan December 25, 1930 location of the poles being possible due to theextremely high coercive force of our improved magnet.

Other objects and particularities of our said invention will be fullyand completely described hereinafter, in connection with theaccompanying drawing, wherein:

Fig. 1 is an elevational view of a simple permanent magnet embodying ourinvention.

Fig. 2 is a sectional end view of the magnet shown in Fig. 1.,

Fig. 3 is an elevational view of a magnet similar to that shown in Figs.1 and 2, but with a different pole-disposition.

Fig. 4 shows diagrammatically a manner in which the magnet shown in Fig.3 is magnetized.

Fig. 5 is an elevation of a horse-shoe magnet embodying our inventionwith its poles at the inner side faces of the two legs.

Fig. 6 is an elevation of a. bar-shaped magnet with a plurality of polesat various parts of the magnet face.

In a preferred embodiment of our invention, powdered material consistingof about 1 mol of ferrous oxide, about 2 'mols of ferric oxide and about1 mol of cobalt oxide is utilized. This powdered material is moulded toany desired shape and dimensions, for example to a simple barshape asshown in Figs. 1 and 2, compressing the material under a suitablehydraulic or mechanical pressure. A quantity of binding material, suchas water glass, may be added if desired to the above-mentioned materialbefore the compression. When the binding material is not used, thecompressing pressure must be about 3000 to 4500 lbs. per square inch inorder to obtain superior results. The pressure may be lower, if thebinding material is utilized. In either case, the compression must beeffected to such a degree that the particles are firmly united togetheror brought into sufficiently intimate contact with each other. After thecompression, the agglomerated body is preferably heated to a.temperature above 600 C. for sintering.

In another desirable embodiment of. our invention, about 2.5 mols offerric oxide and about 1 mol of cobalt oxide are mixed together inpowdered form and the mixture is introduced into a mould wherein it isheated and sintered.

We have found that if the above-mentioned heating is effected in aninert or reducing atmosphere, such as hydrogen, carbon monoxide etc., orin an evacuated vessel, in order to prevent oxidation of the material orto reduce a part of the oxides, the coercive force and retentivity ofthe magnet are materially increased.

The body thus manufactured may be magnetized in a well-known manner, anda permanent magnet is obtained with an extremely high coercive force, ashigh as about five times that of the carbon-steel alloy. We have foundthat if the magnetization is efiected at elevated temperatures, thecoercive force of the magnet is further increased.

In Figs. 1 and 2, a simple bar magnet i is shown embodying ourinvention. It has the north and south poles N and S as in an ordinarypermanent bar magnet. The bar I however, may be magnetized in any othermanner. For example, the poles N and S may be formed on one side of thebar I as shown in Fig. 3. In order to effect such magnetization, amagnetizing device, as shown in Fig. 4, comprising a core 2 and amagnetizing coil 3 woumi thereon, is applied to the bar 8, with its polefaces 4 and 5 in contact with the respective portions of the side faceof the bar I to have N and S poles. The winding 3 is energized from asuitable direct current source, not shown, to produce the necessarymagnetomotive force.

Because of the fact that our ma net has an extremely high coerciveforce, the south and north poles may be formed thereon at any desiredspot or surface, as shown in Fig. 3, and the poles are maintainedpermanently. Fig. 5 shows another example of our magnet, in which ahorseshoe magnet 6 has its poles, N and S, on the inner side faces ofthe ends of both legs. In Fig. 6, a bar-shaped magnet i is shown with aplurality of N and S poles at various parts of its face.

Raw mixture to be utilized in preferred forms of our invention mayconveniently be obtained in any of the following ways.

1st way:l mol of powdered magnetic iron oxide Fe0.Fez03, a compound offerrous oxide, FeO, and ferric oxide, F8203. is mixed with 1 mol ofpowdered ferric oxide and 1 mol of powdered cobalt oxide.

2nd way:1 mol of powdered magnetic iron oxide and 1 mol of powderedcobalt ferrite, COOFGzOs are mixed together.

3rd wayz-l mol of powdered cobalt oxide and 2.5 mols of powdered ferricoxide are mixed together, and 1.5 mols of the ferric oxide containedtherein are reduced to magnetic oxide by heating the mixture in thepresence of a reducing gas, such as carbon monoxide, hydrogen, ammonium,methane, etc. The reduction may be made by heating the mixture in aninert gas, such as nitrogen, or within an evacuated vessel.

. Such reduction occurs because the equilibrium tension of oxygenevolved by the thermal decomposition of ferric oxide is not very lowwhen in the presence of cobalt oxide.

4th way:-1 mol of cobalt nitrate, Co(NO3) 2, or equivalent quantity ofother cobalt salt and 2.5 mols or powdered ferric oxide, or 5 mols offerric nitrate or equivalent quantity of other ferric salt are mixedtogether, and heated to decompose the nitrates or other salts. 1.5 molof the ferric oxide produced by the decomposition are subsequentlyreduced in the same manner as in the 3rd way.

5th way:-1 mol of powdered cobalt oxide and 5 mols of powdered ferricnitrate or equivalent quantity of other powdered ferric salt are mixedtogether, and heated to decompose the nitrates or other salts. 1.5 molof the ferric oxide produced by the decomposition are subsequentlyreduced in the same manner principally as in the 3rd way.

The material obtained by any of the procedures described above is heatedto a temperature above 600 C., and converted to a state suitable forpermanent magnets of the present invention. This heating may bedispensed with if the heating for reduction or decomposition as in thethird to the fifth ways above outlined was eifected at a temperatureabove 600 C. The material thus obtained may be molded to the desiredshape. Altemately, the heating at the temperature above 600 C. may beeffected during the molding operation or thereafter. If the heating atthe temperature above 600 C. is effected after the materialis sumcientlycompressed in the mould, the material is sintered in addition to theabove mentioned conversion into a state suitable for permanent magnets,and the resulting product is a coherent mass or body, While if thisheating is effected before the compression, a second heating ata-temperature above 600 C. is necessary for sintering in order to obtaina coherent mass or body. However, if the binding material is utilized ashereinbefore stated, the second heating at the temperature above 600 C.for sintering is not necessary.

It is not objectionable that the above-mentioned material contain oxidesof copper, zinc, barium, strontium, or magnesium, or a mixture thereofor a small quantity of impurities. Nor is it ohjectionable that itcontains a small quantity of salt or salts of the above-mentionedmetals, but it is preferable to heat the mixture to decompose suchsalts. These oxides or salts contribute to the formation of the coherentbody of the material.

Although the magnetization of the coherent body may be affected at anordinary temperature, it is preferable to efiect the magnetization at ahigh temperature, say at 300 C., prior to the final magnetization atthenormal temperature because we have found that the coercive force andremanence are thereby increased. Such magnetization under heating may beeffected during the sintering process of the body, preferably while notafter sintering.

In place of the oxide of cobalt, oxides of co-. bait and of nickel maybe used. In order to obtain powdered material consisting of oxides ofiron, cobalt and nickel, the above-mentioned five ways may be followedby substituting a part of the cobalt with nickel. A mixture of 1 mol ofmag netic oxide, 1 mol of ferric oxide, a half mol of cobalt oxide and ahalf mol of nickel oxide may also be utilized. The proportions of mixingthe oxides may also be varied. We have found that the introduction ofnickel oxide facilitates the sintering process and increases themechanical property of the magnet. In place of nickel oxide, any otheroxides of metals which facilitate the sintering, such as copper oxide,zinc oxide, chromium oxide, tungsten oxide, etc., may also be used forthe same purpose.

While the invention has been described in considerable detail andspecific examples given, it will be understood that the examples are tobe construed as illustrative and not by way of limitation.

What we claim is:

1. A permanent magnet composed essentially of oxide of iron and oxide ofcobalt.

2. A permanent magnet composed essentially of agglomerated particles offinely comminuted oxide of iron and oxide of cobalt.

3. A permanent magnet composed essentially of ferrous oxide, ferricoxide and oxide 01' cobalt.

4. A permanent magnet composed essentially of oxide of iron, oxide ofcobalt and an oxide of a metal to promote sintering of said oxides.

5. A permanent magnet composed essentially of ferrous oxide, ferricoxide, oxide of cobalt and an oxide of a metal to promote sintering ofsaid oxides.

6. The herein described method oi! manufacturing permanent magnets,comprising mixing together oxide of iron and oxide of cobalt, subjectingsaid oxides to heat to convert the same into magnetic form, subjectingsaid oxides to molding pressure to form a coherent body and magnetizingsaid body.

7. The herein described method of manufacturing permanent magnets,comprising mixing together oxide of iron and oxide of cobalt both inpowdered form, subjecting said mixture to pressure of sufficientmagnitude to agglomerate the particles into a coherent body andmagnetizing said body.

8. The herein described method of manufacturing permanent magnets,comprising mixing together oxide of iron and oxide of cobalt, both inpowdered form, molding said mixture under pressure, heating the moldedbody in a reducing atmosphere and magnetizing said body in the course ofheating thereoi.

YOGORO KATO. TAKESHI TAKEI.

